There are many similarities between business opportunities and franchises but there are also a couple of big differences. Both usually charge you an upfront fee to get involved and offer you help getting your business established.
One of the main differences is that a franchise typically operates under a common brand name and a business opportunity typically does not. Also, most franchises charge ongoing fees and provide ongoing support whereas most business opportunities don't have any formal ongoing support structure and no ongoing fees.
The secret in finding a good one for you--in terms of either choice--is to investigate thoroughly with a significant number of the existing owners. A franchise is required to provide this data to you and in some states so is a business opportunity.
Even if you are in a state without such a requirement, you should never consider any business opportunity that won't provide you with a complete list of their owners for you to call. Be wary of a short "song bird" list of only good validators--you want to be able to talk to any owner in the system at your choice.
Do that and you'll have a good idea if you're getting into one that's right for you.